Endoluminal prostheses may be inserted into a body lumen such as an anatomical vessel or duct for various purposes. Prostheses may maintain or restore patency in a formerly blocked or constricted passageway or they may be used for different procedures. For example, a prosthesis may include one or more stents placed in or about a graft, and the stents may hold the graft in an open configuration to treat an aneurysm. Additionally, stents coupled to one or both ends of a graft may extend proximally or distally away from the graft to engage a healthy portion of a vessel wall away from a diseased portion of an aneurysm to provide endovascular graft fixation.
Stents may be self-expanding or mechanically-expandable or they may have characteristics of both. Preferably, stents may be delivered to a target site in a compressed configuration and subsequently expanded by removing a delivery sheath, removing trigger wires, releasing diameter-reducing ties and/or employing manual stent-expansion techniques. Accurate positioning of stent grafts in a main artery is desirable for a number of reasons such as to avoid occlusion of branch arteries extending from the main artery. Once released from a delivery device, a stent graft with self-expanding stents will assume a position against the vessel wall, making any subsequent repositioning difficult.
Deployment devices are commonly used to position and deploy prostheses, particularly those including self-expanding stents, within various body lumens. In some deployment devices, one or more trigger wires may be used to assist surgeons with the task of positioning stent grafts even after initial release from a deployment device as described herein. In particular, trigger wires can be used to fully or at least partially restrain a prosthesis in a particular position on the deployment device or to restrain one or more self-expanding stents of the prosthesis in a compressed state to facilitate positioning of the stent graft. One such type of trigger wire may be used with one or more diameter reducing ties, which holds two points on the circumference of a graft closer together, effectively reducing the diameter of the graft. The ties are then released, usually by removal of the trigger wire, once the graft is in its intended position. Another such type of trigger wire, which may be referred to herein as a “spiral wire,” secures the graft to a cannula running through the graft lumen. The spiral wire may increase the accuracy of rotational alignment during deployment.